Linkml-model

* Added https://w3id.org/linkml/designates_type

- 25 string serialization
- linkml/linkml177
- 26 recommended field
- 16 unique keys
- 29 docs: clarifying id_prefix docs
- 31 docs: aliases and mappings for metadata elements

This release is compatible with the first working linkml. Next step is to jettison the `biolinkml` dependency and switch to `linkml`